Resistor



Aug. 18, 1936. F. L.. CREAGER RESISTOR Filed Jan. 3l, 1934 Patented Aug.18, 1936 PATENT OFFICE RESISTOE Frederick L. Creager, Camden, N. J.,assignor to Radio Corporation of America, a corporation of DelawareApplication January 31, 1934, Serial No. 709,110

1 claim.v (c1. 2111-16) My invention relates to resistors and moreparticularly to resistors of xed low current value such as thosecommonly used in radio receivers, television apparatus and the like. t

In the manufacture of resistors in large quantities and of all thevarious ohmic values that are required in commercial radio apparatus,considerable difficulty has been experienced in the past in holding eachparticular resistance value to within a reasonable tolerance. As moresensitive circuits are developed, the resistor values become morecritical and consequently their tolerances need continually to bereduced. Under some of the methods practiced in the past, nodetermination of ultimate resistance value could be made until theresistor was nished. The percentage of rejects would, under suchconditions of manufacture, be'excessively high.

Other requirements of a satisfactory resistor for use in radio andtelevision work are such that 1t has been diilicult to produce a lowcost unit which would meet the required specifications and not entailconsiderable expense for equipment,

materials and labor of fabrication. 4

Accordingly, it is one oi the objects' of my invention to produce aresistor in which the conductor has a consistently reproducibleresistance value when manufactured according to low cost quantityproduction methods. u

Another object of my invention is to. provide a resistor, the shape andsize of which may be standardized while the resistance element thereofcan be varied in conductance and current carrying capacity within a verywide range to satisfy Widely varying requirements.

A further object of my invention is to devise a resistor which isimpervious to moisture.

A further object of my invention is to provide resistors which areadapted for attachment singly or in multiple to a base or support byusing the terminal rivets which are an integral part of each resistor.

A further object of my invention is to provide a resistor which can bemanufactured out of low cost materials and with a minimum of processinglabor.

The foregoing objects and other objects which will hereinafter bebrought out I prefer to accomplish by the use of prepared sheet'materialfrom which the elements of the resistor can be blanked out and assembledwith metallic rivets or eyelets, these being pressed into close contactwith an inner lamination or laminations of treated material constitutinga conductor of the desired resistance value. This inner lamination oids.

'may be impregnated with a current conducting medium, or one or bothsides may be provided with a conducting surface iilm applied by coating,5 spraying, or electrical, chemical or electro-chemic a-l deposition.

It is preferred at this time to use graphite and carbon-black as aconducting medium. Modification of the formula and its thickness ofapplica- 10 tion are the rst two controls employed to obtain a givenoverall value ofthe final resistor.

The advantages of using different mixtures of graphite and carbon-blackhave been discussed at length in the co-pending application of Sidney 16Bloomenthal, Ser. No. 699,707, led November 25, 1933, and assigned totheA assignee of the present o invention. Since the subject .matter of'the graphite and carbon-black mixtures as discussed in Bloomenthalsapplication forms no part of the present invention, it is unnecessaryhere to dwell further upon how the resistance element may be l prepared.I After treatment of the inner lamination material to give it thedesired conductive value, the lamination elements are blanked out andthen surrounded by and hermetically sealed within an infusibleinsulating jacket of paper or cloth impregnated with one of the manysynthetic resinso The novel features that I consider characteristic ofmy invention are set forth with particularity in the appended claim. Theinvention itself, however, both as to its organization, the manner ofprocessing the resistor and the objects and advantages to be had fromcarrying out my invention will best be understood from the followingdescription of speciic embodiments when read in connection with theaccompanying drawing in which:

Fig. 1 is a perspective view showing several of the resistors assembledonto a common mounting base, the top of one of the resistors being shownas lifted oi so as to expose to view a notched conductive elementbetween two terminals;

Fig. 2 is an enlarged cross sectional view along the line 2-2 of Fig. 1showing the assembly of the several insulating. and conductinglaminations, together with a pair 01:' rivets and a pair of terminalsfor soldering leads thereto;

Fig. 3 is a plan view of a conducting element which may be used eitheras shown or after reducing its effective width by notching; v

Fig. 4 shows an edgewise view, partly in section, of one of my resistorsto which pigtails may l of a conducting element having an intermediate aconductor wound as va helix about an insulating core to be subsequentlysealed invention.

In order to minimize the cost of manufacturing, I have found that it isdesirable to lperform the various operations of blanking out, as'semlbling and molding the parts of the resistor in such a manner that, asthe resistors are successively finished, they may be immediatelysubjected to test whereby correction may be applied to the subsequentlyprocessed units as quickly as possible so as to bring them within theprescribed limits of variation. d

Accordingly, I prefer to build up my resistor umts out of pieces ofsheet material, one of which is a bottom cover piece i, blanked andperforated for the rivet terminals 2, and a top cover piece 3, blankedbut not perforated. Between the two cover pieces i and l is a smallerstrip 4 which forms the base or core for the conductive material.According to the preferred practice the conductor piece t is firstassembled With the rivets 2 and then with the bottom cover i. These arethen placed in a mold together with the top cover piece 3. All of thelaminations are then subjected to heat and pressure.

The objects to be attained in the molding operation will be betterunderstood by noting that the cover blanks i and 3 are preferably madeof material Which has been impregnated with a synthetic resin, such asphenol formaldehyde or cresol formaldehyde. This resin impregnationpermits polymerizing the cover portions when subjected to heat andpressure and in this manner the top and bottom covers are effectivelysealed together along their edges. The holes in the bottom cover arealso closed up against the Shanks of the rivets 2, so that theconductor, sandwiched between the two cover pieces, is se= curelyincased to protect it from moisture, dirt and rough handling.

After removal from the mold the resistors are .allowed to cool and arethen subjected to test for determiningtheir electrical characteristics.An important feature of the process asvI prefer to carry it out is thatthis testing operation may be performed automatically without thenecessity for handling the resistors individually. When the test is soperformed indications are given as to whether the resistance value iswithin the prescribed tolerances. If not, then a further step of mypreferred processis to be 4carried out. namely to modify the blankingoperation for the cores subsequently utilized in successively fabricatedresistors so that the resistance value may be either increased ordecreased. As an example of how this further step can be accomplished Ishow in Fig. 1 that the resistance element 4 may be blanked out with aplurality of scollops along the edges thereof; while in Fig. 3 I show aresistup in one of the envelopes of my ance element 4a having a givenmaximum Width.

The blanking dies will, therefore, preferably be provided withindependently controllable punches for producing these scollopedformations along apartir the edge. In practice the standard resistancevalue will be obtained as far as possible when punching out twoof thescollops. If, during the automatic testing, it is found that theresistance is too high, then one or more of the notches may 5 beomitted, thereby increasing the cross section of the conductor anddecreasing the resistance value thereof. If, however, the automatictest-- ing operation shows too low a resistance, then a third scollopmay be formed so that the resistance value of the elements so blankedmay be increased. It is of course to be understood that it is entirelywithin the scope of my invention to extend the variation in the blankingof successive resistance elements so that as many notches as desired maybe formed along the edges thereof.

The use of tubular rivets in place of vrivets made from solid rods isentirely within the scope of the contemplated modifications of myinvention. The rivet formed from solid rod material 20 is shown in Fig.2, while a tubular rivet 2a. is shown in Fig. 4.

After testing the resistorsA and rejecting those failing to conform tothe required specifications, those that are acceptable may be assembledon 25 a mounting base 5 as shown in Figs. l and 2. In such .an assemblyany suitable form of terminal clip B may be used for soldering the leadsthereto. Both the resistor and the clips may be held in place byiiangingA a head on the end of each 30` rivet. If the resistor is to beused without mounting on a base plate, it may be preferable to employshort Wires or pigtails i which can be looped around the rivets and thenriveted. crimped or soldered thereto as shown in Fig. 4.

If it is desired to employ a core element both sides of which are coatedwith a conductive lm, then it will be seen that means must be employedby which dependable contacts may be made between the rivets and theopposed film surfaces. To meet this requirement, I have found that a.thin Washer 9 of copper or aluminum foil or the like may be assembled onto the rivets after lnserting the latter through the holes of the-conductor core. When the bottom cover I is then fitted over the rivetsand the complete assembly is placed in the mold for compressing, it willbe seen that both the rivet head and the washer l will be compressedagainst opposite filmed surfaces of the conductor core and in thismanner dependable contact therewith will be established. To insure thatthe best possible contact is made between the washer 9 and the rivet 2or 2a, the hole in the Washer can be made slightly smaller than thediameter of the rivet shank. Then, in forcing the washer onto the rivet,a burr will be formed around the edge of the hole in the washer whichwill cause it to hug the rivet tightly.

While lt is true that for some of the uses to be madex of my resistorsthere would be no appreciable radiation of heat due to the passing of acurrent through the conductor, there are, nevertheless, other uses towhich the resistor may be put in which it is quite desirable that meansbe provided for dissipating the heat generated in such a resistor. Toaccomplish this object corrugations may be made in the mold whereby whenthe resistance unit is compressed therein,V similar corrugations 8 maybe formed on the outer surfaces of the cover blanks as shown in Fig. 5.Even where the corrugations are only about .01" in depth, the increasedareaof radiation has been found to be very effective.

It will, of course, be appreciated that resistors may be made inaccordance with the foregoing disclosure for a very wide variety ofuses, and by various modifications of the process of fabrica--` tion.For example, it is within the scope of my' invention to form theconductive elements of other shapes than those shown, and even to coil aconductor I0 about the insulating core piece il, as shown in Fig. '7,and afterwards to seal this conductor within the polymerized envelope.Furthermore, the resistor may be provided with taps simply byintroducing .additional rivets 2 or eyelets 2a intermediate theelectrical extremities of the resistance element. This last mentionedmodification is illustrated in Fig. 6, which shows a resistance element4b perforated for three rivet terminals, the one to the left beingintermediate the eleftrical extremities of the conductor.

The embodiments of my invention as herein described will be understoodto be more or less illustrative of other embodiments modified to aconsiderable extent without departing from the spirit of my invention.My invention is therefore, not to be limited except insofar as isnecessitated by the prior art and by the scope of the appended claim.

I claim as my invention:

A resistance unit comprising an apertured stripv of material treatedwith a conducting substance and forming an electrical resistanceelement. a plurality of solid rivets each disposed with the head thereofin contact with a portion of said resistance element and the shankthereof extending in a single direction from said element through anaperture in said strip and an envelope of insulating materialhermetically encasing said resistance element and said ilange heads anda portion of the shank of each rivet, the unenveloped portion of eachrivet shank constituting a projecting terminal for connecting said unitin an electrical circuit.

FREDERICK L. CREAGER.

